Electric underfloor heating thermostats and 16A loads

With water underfloor heating, the thermostat only sends a signal to a wiring centre, so a 3A rating is plenty. With electric floor heating, every watt of the mat passes through the thermostat's relay. That is why electric floors need a dedicated thermostat such as the Heatmiser neoStat-e or Slimline-E, both rated at 16A.

This guide shows how to work out the load, what to do when it is over 16A, what the circuit needs, and which thermostat to choose. For choosing the mat itself, see Water vs electric underfloor heating.

Why does an electric UFH thermostat need a 16A rating?

Because it carries the heating current itself. The mat's cold tail connects to the thermostat's load terminals, and the thermostat's relay switches the full current on and off each time the floor calls for heat.

A 3A water UFH thermostat would be overloaded by anything over 690W, which is less than a 5m² mat at 150W/m². The Heatmiser RF-Switch 16A has the current rating but no floor limiting sensor, and Heatmiser state it is not designed for electric underfloor heating.

How do I work out how many amps my heating mat draws?

Add up the wattage of every mat or cable on the thermostat and divide by 230. MaxHeatUFH mats are labelled by area and output, so the wattage is on the size you choose.

1. Measure the free floor area, leaving out units, baths, shower trays and the toilet.
2. Choose the output: 100, 150 or 200W/m² for mats, or set it with cable spacing.
3. Pick the mat or cable sizes and add up their wattage.
4. Divide the total by 230 to get amps.
5. Check the result against the thermostat's 16A rating and the circuit it will be on.

The last row in the table, 4,000W, is over the 16A limit and must be split or switched through a contactor.

What if my electric underfloor heating is more than 16A?

You have two options: split the floor into zones, each on its own thermostat, or use the thermostat to switch a contactor that carries the load. Both need an electrician to design the circuit.

• Split into zones. A 20m² conservatory at 200W/m² can be laid as two 10m² mats, each 2,000W (8.7A), on two thermostats. You also get separate control of each half.
• Use a contactor. The thermostat switches the contactor coil, and the contactor switches the heating. This keeps the room on one thermostat and one floor probe.

Don't run a thermostat close to its limit for long periods. Leaving headroom below 16A, especially in warm rooms such as airing cupboards or behind kitchen units, is good practice.

What circuit does electric underfloor heating need?

Electric floor heating needs RCD protection with a rated residual operating current of 30mA or less. BS 7671, Section 753, which covers floor and ceiling heating, requires this. Heating units with no exposed metal parts also need an earthed metallic grid or screen above them. MaxHeatUFH loose heating cable is twin core with an earth screen.

The circuit itself depends on the load:

These are starting points only. Cable size, protective device and RCD arrangement are for the electrician to design and test.

In England, installing a complete new circuit is notifiable under Part P of the Building Regulations, and so is adding to a circuit in a special location, meaning the area around a bath or shower. A registered competent person electrician can self-certify the work. For bathroom zone rules in detail, see Electric UFH in bathrooms: zones and RCD protection.

Do I need a floor sensor on electric underfloor heating?

Yes. BS 7671 requires floor heating to be protected against overheating, and where people may touch the floor with skin or footwear, the surface temperature must be limited, for example to 35°C. A floor probe lets the thermostat enforce that limit and protect the finish. Both the neoStat-e and Slimline-E include a floor sensor.

• Lay the probe in conduit, midway between two runs of heating cable, not touching or crossing the cable.
• Set the floor limit to suit the finish. Under wood or vinyl, makers commonly set 27°C.
• Test the probe before tiling so you know it reads correctly.

Our guide to floor probes, air sensing and floor limits explains the sensing modes and limits in detail.

Should I choose the neoStat-e or the Slimline-E?

Both switch 16A and come with a floor sensor. Choose the neoStat-e if you want app control or already have a Heatmiser neo system, and the Slimline-E for a lower cost wall thermostat with buttons.

The neoStat-e has self-learning preheat. The Slimline-E has optimum start, holiday, hold and key lock. App control on the neoStat-e needs a neoHub (2nd generation or later). If the house already has one for the water UFH, the electric en-suite joins the same app at no extra hub cost.

Can one thermostat run two electric mats?

Yes, as long as the total load stays within 16A and the mats are connected in parallel by an electrician, following the mat maker's instructions. This is common in L-shaped bathrooms, where one mat won't fit the shape.

Worked example. An L-shaped bathroom has 3m² and 2m² of free floor. A 3m² and a 2m² mat at 150W/m² give 450W + 300W = 750W, or 3.3A. That is well within one Slimline-E or neoStat-e, and well within a fused spur. Only one floor probe is needed, placed in the larger area.

BS 7671 also asks for a plan of each floor heating system, showing the layout, the rated power and the RCD, fixed at or near the distribution board. Photograph the mats before tiling to make that plan easy.

What does a mat and thermostat cost?

Here are three priced examples using MaxHeatUFH 150W/m² mats. Prices inc VAT, October 2026, before tile backer board, membrane and adhesive.

• En-suite, 4m²: 4m² mat (£104) + Slimline-E (£56) = £160. Load 600W, 2.6A.
• Kitchen, 10m²: 10m² mat (£224) + neoStat-e (£83) = £307. Load 1,500W, 6.5A.
• L-shaped bathroom, 5m²: 3m² mat (£77) + 2m² mat (£61) + Slimline-E (£56) = £194. Load 750W, 3.3A.

Products for this job

• Heatmiser neoStat-e electric floor thermostat: £83
• Heatmiser Slimline-E electric floor thermostat: £56
• MaxHeatUFH electric underfloor heating mat 150W/m²: from £41
• MaxHeatUFH electric loose cable, 10W/m or 20W/m: from £14
• 10K floor probe (3m): £13
• Heatmiser neoHub G3: £162
• All electric floor thermostats

Related guides: How to install an electric underfloor heating mat, Heatmiser neoStat vs neoAir vs Slimline and Electric UFH in bathrooms.

Frequently asked questions

Can I use a normal room thermostat for electric underfloor heating?

No. Most room thermostats for water UFH and radiators switch 3A, which is too little for a heating mat. Use a 16A electric floor thermostat with a floor sensor, such as the neoStat-e or Slimline-E.

How many amps does a 10m² electric underfloor heating mat use?

At 150W/m², a 10m² mat is 1,500W, which is 6.5A at 230V. At 200W/m², it is 2,000W, or 8.7A.

Can electric underfloor heating go on a fused spur?

Often, for smaller rooms. A 13A fuse limits the load to about 2,990W at 230V. Larger floors need their own circuit. An electrician should confirm the supply and fit 30mA RCD protection.

What is the maximum area one 16A thermostat can heat?

16A at 230V is 3,680W. That is about 24m² at 150W/m², 18m² at 200W/m² or 36m² at 100W/m², before any headroom.

Do I need an electrician to fit electric underfloor heating?

You can lay the mat yourself, but a qualified electrician must make the final connection, with a 30mA RCD, to BS 7671. A new circuit, or work near a bath or shower, is notifiable under Part P in England.

Can I control electric underfloor heating from my phone?

Yes, with a neoStat-e and a neoHub (2nd generation or later). The Slimline-E has no app or network connection.

Why not use the Heatmiser RF-Switch 16A for floor heating?

It has no floor limiting sensor, so Heatmiser do not design it for electric underfloor heating. Use it for electric heaters, and a floor-sensing thermostat for mats and cable.

Sources: IET Wiring Matters: floor and ceiling heating (BS 7671 Section 753), Approved Document P (gov.uk), Planning Portal: electrics and Part P